clearfog: Update U-Boot to v2018.09-rc3

Change-Id: I1295a79eb8a5b57f1baa8d07f8c5ff46fba6fffe
diff --git a/configs/czechlight_clearfog_defconfig b/configs/czechlight_clearfog_defconfig
index 50150a8..482f07d 100644
--- a/configs/czechlight_clearfog_defconfig
+++ b/configs/czechlight_clearfog_defconfig
@@ -57,7 +57,7 @@
 BR2_TARGET_UBOOT_BUILD_SYSTEM_KCONFIG=y
 BR2_TARGET_UBOOT_CUSTOM_GIT=y
 BR2_TARGET_UBOOT_CUSTOM_REPO_URL="https://gerrit.cesnet.cz/github/trini/u-boot"
-BR2_TARGET_UBOOT_CUSTOM_REPO_VERSION="4aee624c92"
+BR2_TARGET_UBOOT_CUSTOM_REPO_VERSION="v2018.09-rc3"
 BR2_TARGET_UBOOT_PATCH="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/clearfog/patches/u-boot/boot.patch"
 BR2_TARGET_UBOOT_BOARD_DEFCONFIG="clearfog"
 BR2_TARGET_UBOOT_CONFIG_FRAGMENT_FILES="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/clearfog/uboot.fragment"